The invention relates to providing focus information. There are two basic methods of focusing a camera or optical instrument.
In an autofocus system, the camera sets the focus level with little or no user input. The camera collects data about the relative focus level of objects in the camera lens. It uses an algorithm to interpret that data and set an optimum focus level. However, this algorithm does not necessarily execute the photographer's intentions. Many autofocus algorithms prioritize objects that are close to the center of the frame or that are brightly lit. If the object of the photographer's interest is off-center or dimly lit, the autofocus algorithm may calibrate a focus level based on objects in which the photographer has no interest.
Manual focus cameras require more effort from the user. But, they also give the photographer more control over the focus level. Because manual focus cameras are more responsive to the user's wishes and potentially more precise, professionals often use manual focus cameras.
Whichever system a camera employs—autofocus or manual focus—the ability of the system to yield desirable results depends on the user's ability to confirm which objects are in or out of focus. In an autofocus system, if it is unclear which objects are in or out of focus, the user cannot confirm that the autofocus algorithm has identified the user's primary objects of interest and set the focus level accordingly. In a manual focus system, if a user cannot confirm which objects are in or out of focus, the user cannot confirm the precision of focus adjustments.
Camera displays may be too small or imprecise to reliably convey to the user whether or not an object is in focus, or if out of focus, just how much out of focus. They do not often allow the user to distinguish between gradations in the focus level or balance the focus level between multiple objects in the viewfinder.